A fiber-reinforced composite material in which reinforced fibers such as a carbon fiber, a glass fiber, and an aramid fiber and a matrix resin such as an epoxy resin are combined has been developed, and regarding such reinforced fibers, by laminating thin fiber sheets aligned in one direction in multiple directions for use, composite materials with excellent dynamic characteristics can be obtained.
Thus, a technology for aligning, in one direction, the fiber bundle in which a predetermined number of the reinforced fibers are bundled and opening the fiber bundle into a sheet state has been developed. For example, Patent Literature 1 describes a method for opening a reinforced fiber bundle, which, after striking the continuously running reinforced fiber bundle, opens the fiber bundle by using a laterally vibrating roll vibrating in a roll axis direction and/or a vertically vibrating roll vibrating in a vertical direction with respect to a running direction of the reinforced fiber bundle. Patent Literature 2 describes a method for opening a reinforced fiber bundle, which opens a continuously running reinforced fiber bundle by using a lateral vibration imparting roll vibrating in a direction of the reinforced fiber bundle width direction and/or a vertical vibration imparting roll vibrating in a direction crossing the running direction of the reinforced fiber bundle and blows an air flow to a surface on one side and a surface on the other side of a running surface of the reinforced fiber bundle so as to open the reinforced fiber bundle by untangling it. Moreover, Patent Literature 3 describes a fiber opening device which pulls out and supplies fiber bundles from a plurality of yarn feeding bodies, respectively, causes the supplied fiber bundles to run through air flows in a plurality of fluid flowing portions so as to open them in a width direction while bending the fiber bundles by an action of the air flows and by locally bending/stretching the fiber bundles moving at that time so as to alternately and repeatedly change a tension such as stress, relaxation, stress, relaxation and the like.